You have at least two versions of deb-get script in your system:
- A new one supporting Ubuntu 24.04, you downloaded it manually and named
deb-get.sh. - The old one from
deb-get_0.4.0-1_all.debpackage. This one is installed as/usr/bin/deb-getand does not support Ubuntu 24.04.
Here, you are using the newer deb-get script, so it works.
Here, you are using the newer deb-get script to download the latest deb-get_0.4.0-1_all.deb release. Your command works, it installs deb-get_0.4.0-1_all.deb package. During installation, the OLD deb-get script from the .deb package is installed to /usr/bin/deb-get.
Here, you are using the script from /usr/bin/deb-get directly. It's the old one, so it doesn't work. If you want this method to work, you need to replace the script in /usr/bin/deb-get with a new one.